In popular music, half-time is a type of meter and tempo that alters the rhythmic feel by essentially doubling the tempo resolution or metric division/level in comparison to common-time.
Though notes usually get the same value relative to the tempo, the way the beats are divided is altered.
"Half"-time refers to halving this division (divide each measure into quarter notes with the ride pattern), while "double"-time refers to doubling this division (divide each measure into sixteenth notes with the ride pattern).
Some of the variations of the basic groove are notoriously difficult to play on drum set.
In jazz the term means using note values twice as fast as previously but without changing the pace of the chord progressions.